1. Field of the Invention
This invention relates to radiation monitors, and more specifically relates to an electromagnetic radiation monitor which may be worn by persons who may be exposed to potentially harmful levels of electromagnetic energy. Even more particularly, this invention relates to a personal electromagnetic radiation monitor for use in the VHF RF region and which operates substantially independently of polarization.
2. Description of the Prior Art
Attempts have been made to make an electromagnetic radiation monitor which may be worn by a person working in areas where potentially harmful electromagnetic radiation may be present. Early studies, such as those reported by Beischer in his article Microwave Reflection, Diffraction and Transmission By Man, Department of Naval Aerospace Medical Research Lab, Pensacola, Fla., June, 1973, have shown that scattering from a body may produce errors greater than 2 dB. This scattering becomes more significant where broadband frequency performance and independence of polarization are desired monitor characteristics.
U.S. Pat. No. 5,168,265, which issued to Edward E. Aslan, also the inventor herein, discloses a radiation monitor which is independent of polarization and preferably operable between about 2 GHz and about 18 GHz. The radiation monitor senses the electric field component of the electromagnetic radiation and employs thin film resistive thermocouples for this purpose. The radiation monitor disclosed in the Aslan patent mentioned above does not measure electromagnetic radiation in the lower frequency region, that is, well below 2 GHz.
The 1982 American National Standards Institute (ANSI) C95 standard and the Institute of Electronic and Electrical Engineers (IEEE) C95.1 1991 standard require that both the magnetic and the electric fields be measured below 30 MHz, but for frequencies between 30 and 300 MHz, it may be possible through analysis to show that measurement of only one of the two fields, not both, is sufficient for determining compliance with the maximum permissible exposure level.
This frequency range should be monitored, as it coincides with the human resonance region of 30 MHz to 300 MHz where energy absorption in the body is a maximum from both the electric and the magnetic fields. The equivalent power density protection guide in this region is 1 mW/cm.sup.2 or 61.4 volts/meter and 0.163 amp/meter in field strength.
To this date, no practical device being independent of polarization and being responsive to electromagnetic radiation in the VHF RF region, that is, 30 MHz to 1000 MHz, to the knowledge of the inventor, has been successfully marketed.